plugins: remove deprecated code
plugins: remove deprecated code

Since we are only supporting current GStreamer version, since 1.3
gst_buffer_pool_config_add_option() checks if the option to add is
already set. There is no need to do it ourselves.

01org/iotg-lin-gfx-gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,ceyusa/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,GStreamer/gstreamer-vaapi